Many electronic systems include a memory device, such as a Dynamic Random Access Memory (DRAM), to store data. A typical DRAM includes an array of memory cells. Each memory cell includes a capacitor that stores the data in the cell and a transistor that controls access to the data. The capacitor includes two conductive plates. The top plate of each capacitor is typically shared, or common, with each of the other capacitors. The charge stored across the capacitor is representative of a data bit and can be either a high voltage or a low voltage.
Data can be either stored in the memory cells during a write mode, or data may be retrieved from the memory cells during a read mode. The data is transmitted on signal lines, referred to as bit lines, which are coupled to input/output (I/O) lines through transistors used as switching devices. Typically, for each bit of data stored, its true logic state is available on an I/O line and its complementary logic state is available on an I/O complement line.
The memory cells are typically arranged in an array and each cell has an address identifying its location in the array. The array includes a configuration of intersecting conductive lines and memory cells are associated with the intersections of the lines. In order to read from or write to a cell, the particular cell in question must be selected, or addressed. The address for the selected cell is represented by input signals to an address decoder. In response to the decoded address, row access circuitry activates a word line. The selected word line activates the access transistors for each of the memory cells in communication with the selected word line. In response to the decoded column address, column access circuitry selects a bit line. For a read operation, the selected word line activates the access transistors for a given word line address, and data is latched to the selected bit line.
As DRAMs increase in memory cell density, there is a continuing challenge to maintain sufficiently high storage capacitance despite decreasing memory cell size and its accompanying capacitor surface area, since capacitance is a function of surface area. Additionally, there is a continuing goal to further decrease memory cell size.
A principal approach to increasing cell capacitance is through cell structure techniques. Such techniques include three-dimensional cell capacitors, such as trenched or stacked capacitors. One common form of stacked capacitor structure is a cylindrical container stacked capacitor, with a container structure forming the bottom plate of the capacitor. Another method of increasing cell capacitance is through the use of high surface-area materials such as hemispherical-grain polysilicon (HSG) which increase available surface area for a given foot print due to their roughened or irregular surfaces. Additional approaches to increasing cell capacitance may include reducing the thickness of the dielectric layer of the cell capacitor.
As cell size decreases, container structures must be formed in closer proximity to neighboring container structures. At close proximity, care must be taken to avoid shorting the bottom plates of adjacent cell capacitors. Capacitors having such shorted container structures will result in defective memory cells, as the cells will be unable to accurately store data.
For the reasons stated above, and for other reasons stated below that will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for alternative semiconductor container capacitor structures and methods of producing same.